The disclosed invention generally relates to a pulse radar system, and is more particularly directed to a pulse radar system that utilizes a plurality of RF frequencies with a single receiver.
In a typical pulse radar system, the transmitted signal comprises a pulse modulated radio frequency (RF) carrier signal. The pulse repetition frequency (PRF) will depend primarily on the maximum range at which targets are expected since for a given pulse emitted, any corresponding return signal should be received during the receive interval prior to the next pulse in order to avoid ambiguities. In other words, if the pulse repetition rate is too high, the likelihood of receiving target echoes from the wrong pulse transmission (multiple-time-around echoes) is increased.
Thus, unless ambiguous ranges are acceptable, or unless techniques are utilized to distinguish multiple-time-around echoes, which pose other problems, pulse repetition frequencies are reduced with increasing maximum expected range. For applications where the range of interest is further away, for example greater than 40 nautical miles, low pulse repetition rates are utilized and only a small portion of the receive interval is useful. The remaining portion of the receive interval is waiting time that is not utilized.
A known technique for utilizing otherwise non-useful waiting time of the receive interval utilizes a plurality of respectively associated receivers and fixed frequency RF exciters (i.e., each receiver is responsive only to a specific fixed frequency exciter) to permit simultaneous transmit and receive of different frequencies. Performance is improved, but at the cost of additional hardware and complexity.
Performance can also be improved by increasing transmission power. However, this requires larger power supplies, increased power handling capabilities, and in certain applications produces an unwanted increase in interception.